Mechanisms of bone formation and resorption and regulation of parathyroid hormone synthesis and secretion are studied in organ culture. In addition to established hormones, the effect of new agends including prostaglandins and a newly-discovered bone resorbing factor secreted by lymphoytes is being examined. Studies on bone formation include the effects of these hormones and various nutrients on collagen synthesis and calcification. Work on parathyroid hormone synthesis and secretion utilizes rat parathyroid glands in organ culture. The effects of ions and drugs such as chlorthiazide and hormones such as steroids is being examined.